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RGB vs 601/709

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Juan Juig
RGB vs 601/709
on Oct 8, 2015 at 6:40:25 pm

Hello. I find the difference between colour spaces RGB and 601/709 quite confusing. I have been searching for answers to my questions, but I am only more confused then I was.

So, let's say I have footage that was shot in RGB colour space. What happens with the colours if I import the footage and:

1. My import settings are set to: "Computer RGB (0-255)"
2. My import settings are set to: "601 SD or 709 HD"

I read something about Avid always working as if footage were 601/709. Is that correct?

Once you import the footage with certain settings, Avid's source are the MXF files and you cannot change the colour space of the footage within the project. Correct?

Also, when you export the RGB footage (same as source export settings) that you imported as 601/709, as

1. RGB
2. 601/709

What happens with the colours?

I may be asking questions the wrong way. Can someone please explain?


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Job ter Burg
Re: RGB vs 601/709
on Oct 8, 2015 at 7:58:27 pm

I bet this helps:
http://www.jobterburg.nl/Publications/601_709_RGB.pdf.

Do note that 'RGB' can be used for different things. In MC it really means "full swing" or "0-255 (@8bit)".


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Juan Juig
Re: RGB vs 601/709
on Oct 8, 2015 at 8:05:20 pm

I read the whole thing already, before posting as I found it on another post. Could you explain simply and answer my questions?


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Bill Ravens
Re: RGB vs 601/709
on Oct 8, 2015 at 9:13:03 pm

I think the OP is really asking about the diff between RGB and YCrCb. MC used to mis-label things as RGB and 601/709, which is a totally different meaning than color space. In RGB color space, the primaries are carried in 3 channels, one each for R and G and B. In YCrCb, the primaries are carried as Y-luminance, Cr and Cb are mathematical differences in the color signals. Most cameras record in YCrCb. One can mathematically convert from one to the other, but, there are always errors due to roundoffs. Look up the two on Wikipedia for a deeper explanation.



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Michael Phillips
Re: RGB vs 601/709
on Oct 8, 2015 at 9:43:36 pm

With v7 and 8 you can apply a LUT to change color space as needed on source clips.


Michael


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Pat Horridge
Re: RGB vs 601/709
on Oct 9, 2015 at 11:33:30 am

As said by others.

Two things here. Colour Space and levels.

The 601 & 709 spec are 4:2:2 colour space and as such can only carry Y B-Y R-Y signals. These can be derived from RGB signals and converted back to RGB signals.
to carry true RGB values you need 4:4:4 colour space.
HDCAM SR decs use 2 709 inputs (dual link) to achieve 4:4:4:4 (one for alpha) so in that way can record RGBA signals.

So you are describing what information is carried in the digital data. Y, R-Y, B-Y values or R, G, B values.

Then you have the swing levels. TV typically uses 601/709, studio levels which in 8 bit go from 16 to 235. Outside TV typically black is 0 and white is 255 in 8bit. That is often referred to as RGB levels or full swing.

So studio levels, 601/709, for black at 16 white at 235 (8bit)
Full swing, RGB levels for black at 0 white at 255 (8bit)
Just to confuse things 601/709 singles can hold full swing values...

Pat Horridge
Technical Director, Trainer, Avid Certified Instructor
Free online Tutorials at VET digital media academy online http://vimeo.com/channels/752951
VET
Production Editing Digital Media Design DVD
T +44 (0)20 7505 4701 | F +44 (0)20 7505 4800 | E pat@vet.co.uk |
http://www.vet.co.uk | Lux Building 2-4 Hoxton Square London N1 6US


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Juan Juig
Re: RGB vs 601/709
on Oct 9, 2015 at 3:23:53 pm

Thank you for taking time and explaining! :)


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